There's another side to this: what happens when drones become really, really good? Right now they're at about the technological phase that airplanes were in during World War I: nice tools in specific circumstances, but not really overall game changers. But that won't be true for much longer. Advances in drone technology are likely to come pretty quickly, and the result is going to be a very large fleet of drones that are bigger, faster, stealthier, more maneuverable, have better optics, and can accomodate far more — and more effective — weaponry than today's models. And since they're relatively cheap and using them runs no risk of loss of life, there's going to be very little institutional or public pressure against using them. This is likely to mean they'll get a lot of use...

It's not just drones, of course. It's the entire robotic revolution in warfare. When we get to the point where one side is able to conduct war effectively with virtually no fear of loss of life, does that mean that public pressure against war will start to fade away? After all, demand curves slope downward. When war becomes cheaper, we'll get more war. Right?

That argument would hold only if cheaper war would be as satisfying as expensive war. And it probably wouldn't be.

Let's back up. While it seems obvious that drones may have an effect on the supply side of war--supply becomes cheaper--they could also dampen the demand for war. Now it may seem strange to talk about the demand for war but it really shouldn't. Like everything else, we get war because there is a demand for it.

Sometimes the source of the demand is special interest rent seeking--Anglophiles wanting to beat back the Huns or imperialists wanting to push Spain out of the hemisphere. That type of demand probably won't be diminished by wars being fought with drones.

But there's another type of war demand that probably would be. That's the popular war demand, the "war fever" that has been witnessed countless times through the ages. A key factor of this demand is the manliness of fighting wars: bravery in the face of battle, iron in the blood forged in the furnace of fighting. Drone warfare simply won't satisfy this demand, which would me that a wars get cheaper to fight they also get less interesting to fight.

Something along these lines seems to have happened with the last round of innovations in war fighting. Bombers and tanks made a lot of traditional warfare obsolete. Instead of coming home from the trenches of World War I with tales of derring-do that might inspire the next generation to seek their own war, WWI vets seemed to have taken a dim view of their war. And that worked: the Europeans only fought one more war against each other that century.

Of course, fewer wars might not actually be an improvement if the wars we get wind up being as bad as the two Europe fought in the last century.